Handling Set Up and Driving Theory

[Big Supes]

Just for the purpose of conversation, something I've been thinking about since deciding to up the power on my car is rear end traction and overall control of the car once the rear tyres have broken loose under power. 

Some RWD cars break traction under power (in a straight line) and all you notice is the rpm shoot up like a clutch slip, while others will suffer, what I can only describe as 'Mustang Syndrome' and immediately kick sideways. 

My car falls somewhere between the two. It'll kick sideways, especially if I'm going up a level hill in a straight line, but it's catchable. Tbh, I'd rather it didn't want to send us into a ditch in the first place though. 

I'm thinking the diff might need servicing or maybe that's just how it is. I've replace all the sloppy suspension arms/bushes and running new coilovers so hoping that should make a difference. 

I'm sure someone who knows a great deal more than me about geometry and handling will be able to shed some light on it. 

[mattdavies]

What sort of power are you running currently ? What size tyres ? what brand etc ? What coilovers are you running ? 

 

I am BPU auto @ 400bhp est. I have run Bilstein Shocks and Eibach Springs for many years now on a few different tyres. all 255/40 or 35/ 18 and I would say on Potenza's and my current Goodyears I dont really have many traction issues at all. Having said this when i does break traction it does go sideways fairly quickly and I have to catch it as it will be round in no time. 

 

I am on an Open diff but dont think an LSD would make much difference 95% of the time when talking traction 

Edited October 28, 2021 by mattdavies (see edit history)

[Frank Bullitt]

You need to get in touch with Chris Wilson for geometry and handling. It’s his bread and butter.

If you’re not running the standard 17” rears and you are on 18”s, you should have a 40 rear profile. Sidewall is key to grip. Also fit decent tyres, anything from Michelin’s top lines is great and they offer decent wheel protection too.

The OEM torsen is okay but going to a 1.5 way plate OS Giken would be night and day.

New engine, gearbox, diff mounts and the rubber doughnut would also help.

[Frank Bullitt]

@Chris Wilson

[Big Supes]

5 hours ago, Frank Bullitt said:

You need to get in touch with Chris Wilson for geometry and handling. It’s his bread and butter.

If you’re not running the standard 17” rears and you are on 18”s, you should have a 40 rear profile. Sidewall is key to grip. Also fit decent tyres, anything from Michelin’s top lines is great and they offer decent wheel protection too.

The OEM torsen is okay but going to a 1.5 way plate OS Giken would be night and day.

New engine, gearbox, diff mounts and the rubber doughnut would also help.

Thanks Frank. I'm currently running stock 17's, but will be swapping to 18's soon so I'll bare in mind the tyre profile. I'm opting for michelin pilot sport 4's. A friend runs them and vouches for them. I've also read/seen nothing but good things about them via online reviews and videos. 

OS Giken has been on the radar for a while and I'm looking to drop the rear subframe this winter for inspection, clean up and fresh powder coat. Since converting to manual I've noticed the diff mounts definitely need doing. The new gearbox is solid (poly) mounted so it has exposed/off loaded onto the other mounts. I think I'll take your advice and add to the list with engine mounts as well.

7 hours ago, mattdavies said:

What sort of power are you running currently ? What size tyres ? what brand etc ? What coilovers are you running ? 

 

I am BPU auto @ 400bhp est. I have run Bilstein Shocks and Eibach Springs for many years now on a few different tyres. all 255/40 or 35/ 18 and I would say on Potenza's and my current Goodyears I dont really have many traction issues at all. Having said this when i does break traction it does go sideways fairly quickly and I have to catch it as it will be round in no time. 

 

I am on an Open diff but dont think an LSD would make much difference 95% of the time when talking traction 

I'm around 450 at the fly, but to be honest, it's mainly in the wet that I notice how the rear generally wants to kick to the right when I jump on it. 

Admittedly, this was A LOT worse before recently fitting poly bushed rear upper arms and fitting new coilovers (hsd monopro). 

In my experience, open diff is night and day to an LSD. A lot more forgiving as you generally still have 50% traction at the rear as one wheel will always stop spinning or fail to start in the first place. 

5 hours ago, Frank Bullitt said:

 

 

[Frank Bullitt]

1 hour ago, Big Supes said:

Thanks Frank. I'm currently running stock 17's, but will be swapping to 18's soon so I'll bare in mind the tyre profile. I'm opting for michelin pilot sport 4's. A friend runs them and vouches for them. I've also read/seen nothing but good things about them via online reviews and videos. 

OS Giken has been on the radar for a while and I'm looking to drop the rear subframe this winter for inspection, clean up and fresh powder coat. Since converting to manual I've noticed the diff mounts definitely need doing. The new gearbox is solid (poly) mounted so it has exposed/off loaded onto the other mounts. I think I'll take your advice and add to the list with engine mounts as well.

Re the Michelin’s make sure you can get the tyre size you want in the width you want. I looked at a set of custom wheels (17x10) rears but the selection was non existent in a 285/40/17.

The mixture of poly and rubber OEM maybe a reason for things feeling different too, they will both react differently due to being different materials.

[Annabella]

Think Mr Wilson will recommend you stay on 17's. And as Frank says won't like the mix of poly and oem.

[Burna]

9 hours ago, Frank Bullitt said:

Re the Michelin’s make sure you can get the tyre size you want in the width you want. I looked at a set of custom wheels (17x10) rears but the selection was non existent in a 285/40/17.

The mixture of poly and rubber OEM maybe a reason for things feeling different too, they will both react differently due to being different materials.

That profile size is too big mate  for a 275 it's a 35 profile.

[Burna]

Now I'm no Chris Wilson, so please don't quote me on this lol But I once was told the reason it kicks the same way all the time is because the drive shafts from the diff to the wheels are different lengths on either side.

No idea if that's the reason, but just throwing it out there lol

[Big Supes]

2 hours ago, Burna said:

Now I'm no Chris Wilson, so please don't quote me on this lol But I once was told the reason it kicks the same way all the time is because the drive shafts from the diff to the wheels are different lengths on either side.

No idea if that's the reason, but just throwing it out there lol

Now you say that, I have that theory before lol.

11 hours ago, Frank Bullitt said:

Re the Michelin’s make sure you can get the tyre size you want in the width you want. I looked at a set of custom wheels (17x10) rears but the selection was non existent in a 285/40/17.

The mixture of poly and rubber OEM maybe a reason for things feeling different too, they will both react differently due to being different materials.

 

10 hours ago, Annabella said:

Think Mr Wilson will recommend you stay on 17's. And as Frank says won't like the mix of poly and oem.

Just to clarify, the handling has improved since changing out the rear upper arms for poly and changing the suspension to coilovers. 

The car was at its worst when it was on stock suspension with lowering springs. 

[Style]

I never really knew too much about how common snapping right under lighting up the rears was. Glad it's not just me!

[Frank Bullitt]

3 hours ago, Burna said:

That profile size is too big mate  for a 275 it's a 35 profile.

A 10” rear will take a maximum of a 285 tyre, it will also take a 275, 265 and a 255. 265 & 255 will be stretched

I know the profile is supposed to be a 35 to keep within stock radius but if you want more traction and a smoother ride on the rear, a 40 fits fine and works wonders. Increasing from a 17” to an 18” and wanting to keep the feel of the car the same meant I had to keep the sidewall the same. Hot rod tuning 101. You need a decent tyre wall.

I didn’t go with custom rears (17x10) due to tyre choice but added a 40 profile on the rear 18” wheels with lovely results.

[Frank Bullitt]

1 hour ago, Big Supes said:

Just to clarify, the handling has improved since changing out the rear upper arms for poly and changing the suspension to coilovers. 

The car was at its worst when it was on stock suspension with lowering springs. 

So original worn OEM components replaced with poly? Makes sense for the improvement.

Regarding unequal length drive shafts, the longer shaft is going to ‘wind up’ more than the shorter one, so the wheel on that side experiences a “lagging” effect and therefore less torque (because some of it is being used to twist the shaft). The other wheel will pull harder, so the car will tend to turn towards the side with the longer shaft.

 

[Frank Bullitt]

^ I think the last part is correct but if someone knows better please correct me.

[mattdavies]

6 minutes ago, Frank Bullitt said:

A 10” rear will take a maximum of a 285 tyre, it will also take a 275, 265 and a 255. 265 & 255 will be stretched

 

I am sorry but the statment above isnt true, a 255 on a 10" isnt stretch at all and I believe I have seen it as OEM fitment on some Porsches. I run a 255/40/18 on a 18x10 ET20 rear wheel, I rarely have traction issues. 

I have also run a 225/40/18 on the same size wheel up front and had no issues 

[Frank Bullitt]

1 minute ago, mattdavies said:

I am sorry but the statment above isnt true, a 255 on a 10" isnt stretch at all and I believe I have seen it as OEM fitment on some Porsches. I run a 255/40/18 on a 18x10 ET20 rear wheel, I rarely have traction issues. 

I have also run a 225/40/18 on the same size wheel up front and had no issues 

 

[Burna]

I find the correct profile of 35 on a 275 rear is better for handling, less tyre roll when pushing it in corners hard.

[Frank Bullitt]

2 minutes ago, Burna said:

I find the correct profile of 35 on a 275 rear is better for handling, less tyre roll when pushing it in corners hard.

That is why handling and tyre recommendation is subjective (unless the individual involved is a dumb dumb) as it’s based on personal opinion and choice. I am not sure how noticeable 5% is but to you and I it feels different. More comfortable and predictable to me but more tyre roll to you

It’s all down to what an individual likes.

[rider]

I found excellent professional help with a chassis tune setup after my car underwent a complete new suspension, arms and bushing overhaul. I used Center Gravity in Warwickshire to set my new parts and they spent a lot of hours setting up the handling to my preferred driving style which I requested due to my age and wisdom as planted grandad tourer with slightly heavier steering. The difference was very noticeable in a good and positive drive way over the in the right region settings for the new parts.

As well as all the tracking and steering geometry setting they will check that the ride height is true and shim if required to give the perfect weight distribution front to rear and cross axle which would be a key determinant in any under power side stepping. It wasn't cheap but they spent a long time on the car fettling and fine tuning then road testing my grandad setup. 

[Big Supes]

20 hours ago, rider said:

I found excellent professional help with a chassis tune setup after my car underwent a complete new suspension, arms and bushing overhaul. I used Center Gravity in Warwickshire to set my new parts and they spent a lot of hours setting up the handling to my preferred driving style which I requested due to my age and wisdom as planted grandad tourer with slightly heavier steering. The difference was very noticeable in a good and positive drive way over the in the right region settings for the new parts.

As well as all the tracking and steering geometry setting they will check that the ride height is true and shim if required to give the perfect weight distribution front to rear and cross axle which would be a key determinant in any under power side stepping. It wasn't cheap but they spent a long time on the car fettling and fine tuning then road testing my grandad setup. 

That sounds like a great investment/time and money well spent. I hadn't given much thought about the C of G in terms of weight distribution under power, but it makes perfect sense in terms of power delivery and also braking performance. 

When setting up race boats back in the day when I was a marine engineer, the C of G was a pretty important factor in giving a boat the edge over another that appears (by the rules) to be identical. Sort of like stock car racing but with boats. 

While I'm not looking to go all out on this by throwing out the interior and any unnecessary parts for weight saving, I do see a lot of mileage in a decent street car set up.

[Big Supes]

22 hours ago, Frank Bullitt said:

So original worn OEM components replaced with poly? Makes sense for the improvement.

Regarding unequal length drive shafts, the longer shaft is going to ‘wind up’ more than the shorter one, so the wheel on that side experiences a “lagging” effect and therefore less torque (because some of it is being used to twist the shaft). The other wheel will pull harder, so the car will tend to turn towards the side with the longer shaft.

 

That's correct mate. My rear upper arms were pretty soggy and I had some poly bushes kicking around that I had bought years ago so I swapped the old OE bushes out for them. 

Ah yes, that's what I remember hearing a while back re the unequal drive shaft lengths. I wonder if there is a way to combat this effect? I'm wondering if both can be balanced via being made to be the same weight. 

[Frank Bullitt]

3 hours ago, Big Supes said:

That's correct mate. My rear upper arms were pretty soggy and I had some poly bushes kicking around that I had bought years ago so I swapped the old OE bushes out for them. 

Ah yes, that's what I remember hearing a while back re the unequal drive shaft lengths. I wonder if there is a way to combat this effect? I'm wondering if both can be balanced via being made to be the same weight. 

Other than making sure all suspension components are 100% along with the alignment (as rider mentioned above) I don’t think there is much you can do as it’s the nature of the beast. Torque steer is what is it but should not happen unless under full/heavy drivetrain load, unequal length shafts or not.

You can test the alignment by driving at a reasonable speed then put the car into neutral. The gearbox and drivetrain will not be seeing any power so the Supra should keep a straight line without any hands on the steering wheel. Make sure that there is no crown down the centerline of the road, it needs to be perfectly flat. If the Supra pulls to one side while in neutral then the alignment is off. If the Supra pulls when applying the brakes, then the brakes are off.

All you can do is make sure you have everything as it should be which includes decent offsets (as close to OEM as possible) on the wheels, don’t ever consider 19”s unless you like driving in a ditch, use a decent branded and correctly sized street tyre (not the rubber band stretch type), the correct PSI, good suspension, driver knowledge and experience. Also make sure to keep both hands on the steering wheel.

That OS Giken (1.5 way) I mentioned is a good addition too. 

Have you ever done a good advanced driver course before? They cost the Earth but are worth their weight in gold.

I wouldn’t consider unbalancing one to make it behave differently to how Toyota intended as I’d imagine that could cause unnecessary wear and stress to other supporting components. Money no object, you could fit a 4x4 system but it will zap power (due to all four wheels being driven) and the conversion will empty your wallet quicker than a 7 second Supra.

Have you managed to touch base with the Geometry Oracle in deepest darkest Shropshire yet? Chris will be able to give you a much better, more in-depth knowledge based answer from many years hands on experience.

Edited October 30, 2021 by Frank Bullitt (see edit history)

[Big Supes]

22 hours ago, Frank Bullitt said:

Other than making sure all suspension components are 100% along with the alignment (as rider mentioned above) I don’t think there is much you can do as it’s the nature of the beast. Torque steer is what is it but should not happen unless under full/heavy drivetrain load, unequal length shafts or not.

You can test the alignment by driving at a reasonable speed then put the car into neutral. The gearbox and drivetrain will not be seeing any power so the Supra should keep a straight line without any hands on the steering wheel. Make sure that there is no crown down the centerline of the road, it needs to be perfectly flat. If the Supra pulls to one side while in neutral then the alignment is off. If the Supra pulls when applying the brakes, then the brakes are off.

All you can do is make sure you have everything as it should be which includes decent offsets (as close to OEM as possible) on the wheels, don’t ever consider 19”s unless you like driving in a ditch, use a decent branded and correctly sized street tyre (not the rubber band stretch type), the correct PSI, good suspension, driver knowledge and experience. Also make sure to keep both hands on the steering wheel.

That OS Giken (1.5 way) I mentioned is a good addition too. 

Have you ever done a good advanced driver course before? They cost the Earth but are worth their weight in gold.

I wouldn’t consider unbalancing one to make it behave differently to how Toyota intended as I’d imagine that could cause unnecessary wear and stress to other supporting components. Money no object, you could fit a 4x4 system but it will zap power (due to all four wheels being driven) and the conversion will empty your wallet quicker than a 7 second Supra.

Have you managed to touch base with the Geometry Oracle in deepest darkest Shropshire yet? Chris will be able to give you a much better, more in-depth knowledge based answer from many years hands on experience.

I think your post pretty much summarises the sensible approach to upping the power. In a nutshell, make sure the car is set up correctly and get some experience whether it's on a track, driver course etc. I guess I was more interested in the cause and effect of why something is happening. I'm going to look into geometry as an interest, but have my car set up by a specialist to my requirements. 

I haven't spoken to Chris. It's a real shame he's so far away as I'd drop my car off with him and get it set up. 

Regarding driver courses, I'd be keen to do some events where you can take your cars on a runway or track with a nice amount of runoff and find the limit of the car in the higher gears. I have no real interest in advanced driver courses that have any element of the road safety. I've done my fair share of driver awareness courses.

[rider]

A good chassis tune company will set up the car to your desired handling and steering characteristics. Its of course easier to do if you have adjustable parts which don't come on a standard car; like adjustable springs, and multi-hole sway bars. A good company will talk you through what you are hoping to achieve and even tell you the consequences of a desired setup - like it'd be no good in the wet or on cambered public roads etc. That is why everything is a compromise unless a car has a specific home environment, like say a dedicated track car. That is also where having adjustable parts helps over stock parts as they could advise you two turns for this use and one hole back for that use so you can set the car to a specific but different environments.

As for places being too far away, there are always hotels and B&B's. I stayed in a fantastic B&B the night before my car went to Center Gravity. A room in a country mansion overlooking the even bigger country estate house and a massive duck pond that was the size of a small house and top breakfast all for £55. Its worth finding a good place that will work with you to develop your ideal setup than heading somewhere because it happens to be close to home. The Center Gravity company I used does mainly Porsche cars and they get gushing reviews on Porsche club forums and on the likes of Google from owners. The company owner has a bit of a soft spot for Mk4 Supras though. Even the son of the B&B owners, who is a scooby fan himself, spent half an hour fawning over my car revealing his JDM views that its so much better than all those pretentious Porches that they have visit their establishment on the way to Center Gravity. 

Choose wisely, pay over a few Hundred for the privilege and if you get the right place you'll be under the car with them while they set up the car and they will be educating you by explaining what each change they make as they make it will do to the cars handling. I haven't had some much fun spending 4 hours underneath my car watching others do the work whilst educating me along the way. There are places that want the owners involved and fully engaged, its called passion for what they do.

[Frank Bullitt]

On 10/31/2021 at 9:46 AM, Big Supes said:

I think your post pretty much summarises the sensible approach to upping the power. In a nutshell, make sure the car is set up correctly and get some experience whether it's on a track, driver course etc. I guess I was more interested in the cause and effect of why something is happening. I'm going to look into geometry as an interest, but have my car set up by a specialist to my requirements. 

I haven't spoken to Chris. It's a real shame he's so far away as I'd drop my car off with him and get it set up. 

Regarding driver courses, I'd be keen to do some events where you can take your cars on a runway or track with a nice amount of runoff and find the limit of the car in the higher gears. I have no real interest in advanced driver courses that have any element of the road safety. I've done my fair share of driver awareness courses.

At just over a 370 mile one way trip from me to Chris I know what you mean about distance but pick up the phone a chat with him.

I won’t ask re the DAC but this Milbrook course look pretty good - https://www.total-car-control.co.uk

Edited November 1, 2021 by Frank Bullitt (see edit history)