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Spring rate/ length 
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GTM delivered

Joined: Mon Apr 17, 2017 10:05 pm
Posts: 38
Location: Bristol
GTM: Libra
Post Re: Spring rate/ length
Thank Sanzo,
Yep, I'm getting mine from Mike S, LHD and good price for a new unit.


Tue Oct 12, 2021 8:49 pm
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GTM Nirvana
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
I posted some pics a long time ago - there is a section on the input shaft that is flat on the metro one but splined on the TF one. It is where the pinch bolt goes through. A couple of splines need grinding flat over a 6mm section or so IIRC otherwise when you try to get the pinch bolt through you'll find you can't and as that'll be with your arm through the access hole down by the pedals you'll curse. Compare the two before you install the new one and you'll see.


Tue Oct 12, 2021 9:53 pm
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Part built GTM

Joined: Sat Oct 22, 2016 12:41 am
Posts: 126
Location: Brisbane Australia
GTM: Spyder
Post Re: Spring rate/ length
sanzomat wrote:
Tyre pressures I've found work best:
Road (205/45/15 all round) 18psi front 22 rear
Track semi's (195/50/16 front, 225/45/16 rear) 16psi front 20 rear
Track slicks (200/580/16 front, 210/610/16 rear) 16psi front 18 rear.

These are all cold pressures. When it gets really hot I let a bit out but I find if I start lower it feels a bit unsure for the first couple of sessions in the morning. When I re-check them (if I remember to) after they've cooled back down they end up as 15 front and 16 rear. When fully hot they increase by about 6psi on the rears i.e. 22 hot

Did the "track" pressures produce the best times? They are surprisingly low.


Thu Oct 14, 2021 2:38 am
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GTM Nirvana
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
Yep, those are what I found gave the best times (trial and error) although on UK track days you aren't allowed to time your laps so obviously only discovered later when analysing the video. No phone apps where ever used :wink:


Thu Oct 14, 2021 7:53 am
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Part built GTM

Joined: Sat Oct 22, 2016 12:41 am
Posts: 126
Location: Brisbane Australia
GTM: Spyder
Post Re: Spring rate/ length
So I will be tracking (1 lap autocross) with semi-slicks 205/45/16 all round. From your numbers (16-F 20-R) I am thinking to start at 16-F 22-R


Thu Oct 14, 2021 11:17 pm
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GTM Nirvana
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
If you only have one lap you may need to start a bit higher. I usually take the first lap a bit steady to warm the tyres (which increases the pressure a bit). If you don't have a warm up lap the cold pressures would need to be higher as they'll still be cold for most of that lap. I'd go 18F 22R in that situation


Fri Oct 15, 2021 9:47 am
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Part built GTM

Joined: Sat Oct 22, 2016 12:41 am
Posts: 126
Location: Brisbane Australia
GTM: Spyder
Post Re: Spring rate/ length
sanzomat wrote:
Tyre pressures I've found work best:
Road (205/45/15 all round) 18psi front 22 rear
Track semi's (195/50/16 front, 225/45/16 rear) 16psi front 20 rear
Track slicks (200/580/16 front, 210/610/16 rear) 16psi front 18 rear.

These are all cold pressures. When it gets really hot I let a bit out but I find if I start lower it feels a bit unsure for the first couple of sessions in the morning. When I re-check them (if I remember to) after they've cooled back down they end up as 15 front and 16 rear. When fully hot they increase by about 6psi on the rears i.e. 22 hot
Hi Sanzomat. Do you have GAZ dampers? I ran another autocross day with the new tyres. Tyre grip was improved but not to the level I expected. Tyres were definitely not getting up to temperature (50 - 60 seconds per run).

I am still running what I think are fairly soft settings on the dampers, about 10 clicks (of 28?) on the rear and 8 on the front. It wasn't until after the event that I realised I should have tried firming them up - maybe next time. Can you offer any guidance on street vs track settings?


Mon Nov 08, 2021 11:47 pm
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GTM Nirvana
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
Yes, Gaz dampers on the GTM. I thought they only go up to 20 clicks but could be wrong. I use 8 clicks front, 10 rear on the road and add two clicks all round for track days. Any more than that and they start to jack down!

I'm not surprised your tyres aren't getting to temperature on 1 minute runs. Mine (either slicks or semi's) take at least a whole lap of Combe to start to grip well (around 90 seconds) for the first half a lap it feels very nervous and you have to corner and brake quite gently and then build up. The left handers (only 2 at Combe) on the second lap can be scary as the right side tyres take longer to warm up. When I do Llandow circuit, only 45 seconds laps, it doesn't grip properly until well into the second lap and that has a very abrasive surface.


Tue Nov 09, 2021 10:50 am
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