Suspension setup - Rear damper travel
Discussion
I recently had a 2 hour 'health check' of the suspension on my Tamora done by Chris at Centre Gravity. He seems to be well-respected for car setups both for road use and for race, and has worked on a few TVRs including people from this forum who rate his work.
I had this done as I was curious about a few things, including getting an accurate weight for the car, but have also found the ride to be a little too twitchy at times on B roads.
With a full tank of fuel, and no driver, the Tamora weighed 1124kg (the car has air-con). With the addition of a driver, weight balance was 50/50 front/back but corner weights were off.
The most concerning thing we noted was the lack of rear damper travel. The car has a Gaz Gold Pro setup which is quite recent (July 2011, 5000 miles ago), and was installed by a TVR Specialist.
When looking at the front dampers they had a few cm of travel and a dirty area on the damper rod where they did not quite reach the bump stop.
However, the rear dampers only had 15mm of travel left with the car empty, and 10mm with a driver. The damper rod looked shiny right up to the bump stop.
This seems to me to be too little damper travel.
The amount of damper travel must be set by 2 factors:
1) The car ride height
2) The length of the damper
For 1 - The ride height of the car is at, I believe, the upper-end of Tamora ride heights, see the pics below and I also have some measurements to parts of the chassis.
For 2 - This is the standard damper fitted to the rear of the Tamora by Gaz.
Discussions are ongoing with Gaz about options for the rear damper / springs. The current suggestion is the fitment of a shorter bump stop combined with stiffer springs.
When hitting big bumps the car can rub the rear wheel on the wheel arch (this has happened 5 times in 5000 miles). I have set the rear damping a little too firm to help avoid this. I don't really want much more suspension travel to avoid rubbing, but equally I don't think the ride height should be higher...
Current spring rates are 400 lb/in front and 325 lb/in rear. I understand this is too low on the rear and it should be 350 or 375.
Given the rear springs are at more of an angle from vertical from the front, the effective spring rate would be less than that rated number, although there are plenty of other factors that I don't know including how the mounting points differ front to back to change the effective spring rates at the wheel.
I believe the rear should be slightly softer-sprung than the front - What rates are others using? I have heard of people going as high as 500/400. It may be better with stiffer springs and a little less damping.
Any advice and opinions welcome.
I had this done as I was curious about a few things, including getting an accurate weight for the car, but have also found the ride to be a little too twitchy at times on B roads.
With a full tank of fuel, and no driver, the Tamora weighed 1124kg (the car has air-con). With the addition of a driver, weight balance was 50/50 front/back but corner weights were off.
The most concerning thing we noted was the lack of rear damper travel. The car has a Gaz Gold Pro setup which is quite recent (July 2011, 5000 miles ago), and was installed by a TVR Specialist.
When looking at the front dampers they had a few cm of travel and a dirty area on the damper rod where they did not quite reach the bump stop.
However, the rear dampers only had 15mm of travel left with the car empty, and 10mm with a driver. The damper rod looked shiny right up to the bump stop.
This seems to me to be too little damper travel.
The amount of damper travel must be set by 2 factors:
1) The car ride height
2) The length of the damper
For 1 - The ride height of the car is at, I believe, the upper-end of Tamora ride heights, see the pics below and I also have some measurements to parts of the chassis.
For 2 - This is the standard damper fitted to the rear of the Tamora by Gaz.
Discussions are ongoing with Gaz about options for the rear damper / springs. The current suggestion is the fitment of a shorter bump stop combined with stiffer springs.
When hitting big bumps the car can rub the rear wheel on the wheel arch (this has happened 5 times in 5000 miles). I have set the rear damping a little too firm to help avoid this. I don't really want much more suspension travel to avoid rubbing, but equally I don't think the ride height should be higher...
Current spring rates are 400 lb/in front and 325 lb/in rear. I understand this is too low on the rear and it should be 350 or 375.
Given the rear springs are at more of an angle from vertical from the front, the effective spring rate would be less than that rated number, although there are plenty of other factors that I don't know including how the mounting points differ front to back to change the effective spring rates at the wheel.
I believe the rear should be slightly softer-sprung than the front - What rates are others using? I have heard of people going as high as 500/400. It may be better with stiffer springs and a little less damping.
Any advice and opinions welcome.
What did Chris at Centre Gravity actually recommend/suggest ?? Does sound like the rear shocks aren't long enough and/or the springs are too soft from your diagnosis above, but I no very little (nothing really) about suspension dynamics.
I would say that your ride height is as high 'cosmetically/aesthetically' as you would want. Any higher and it will look wrong. It could probably be with being a little lower actually, so the wheels follow the wheel arches a bit better, but again, that's cosmetic, not suspension dynamics.
I had the Sag ride height increased so I could stop taking all the paint of the diffuser and splitters getting on and off my drive and over speed bumps etc., and over very bumpy b-roads at speed, something rubs occasionally, and my T350 used to bottom out a hell of a lot even on the M40 through Oxfordshire, so perhaps they all have this generic design problem.
I would say that your ride height is as high 'cosmetically/aesthetically' as you would want. Any higher and it will look wrong. It could probably be with being a little lower actually, so the wheels follow the wheel arches a bit better, but again, that's cosmetic, not suspension dynamics.
I had the Sag ride height increased so I could stop taking all the paint of the diffuser and splitters getting on and off my drive and over speed bumps etc., and over very bumpy b-roads at speed, something rubs occasionally, and my T350 used to bottom out a hell of a lot even on the M40 through Oxfordshire, so perhaps they all have this generic design problem.
The standard Tamora does not suffer from a lack of travel at the raer, but it does benefit from the fittment of a stiffer slightly shorter spring. I went for Tuscan S rear springs, standard fronts and Billstiens allround on my good ladies car and the rear feels to work better.
Riding around on the bump stops should not be the case unless someone has lowered the car? Have the Gaz shocks got an adjustable platform?
Riding around on the bump stops should not be the case unless someone has lowered the car? Have the Gaz shocks got an adjustable platform?
RedSpike66 said:
What did Chris at Centre Gravity actually recommend/suggest ??
- Dampers look too long (if there is little travel left when the car is static) - see if Gaz can supply shorter dampers. Apparently these dampers should be fine on a Tamora.- Springs are probably too soft (backed up by discussions with Gaz)
- A number of other little things with the setup that I haven't detailed here
I agree that the ride height should;t be any higher. It seems to be ok for avoiding scraping on things. Any higher and it would look odd.
I am not sure if the Tamora front splitter is lower than the Sagaris front.
RedSpike66 said:
my T350 used to bottom out a hell of a lot even on the M40 through Oxfordshire, so perhaps they all have this generic design problem.
Could be. Any other T350 / Tamora owners able to comment?TVR_owner said:
The standard Tamora does not suffer from a lack of travel at the rear, but it does benefit from the fittment of a stiffer slightly shorter spring.
Agree about the stiffer spring. Not sure about the shorter spring.TVR_owner said:
Riding around on the bump stops should not be the case unless someone has lowered the car? Have the Gaz shocks got an adjustable platform?
The car is fairly high for a Tamora (IMO) - I hope the pictures above illustrate that,The Gaz shocks do have an adjustable spring platform. But the shocks just seem to be a bit long.
The only way to get more damper travel on these Gaz dampers is to:
- further raise the ride height
- get a small amount extra by fitting a shorter bump stop (current one is ~ 5cm) and stiffening the springs so it is less likely to reach it.
Anybody else running a Gaz Gold pro kit on a Tamora / T350 and had a look at their suspension in this much detail?
TVR_owner said:
Sag sits lower at the front than a Tamora (standard vs standard)
Tamora seemed plenty low to me...When I first got the car, I scraped the centre of the front splitter on a 3" / 75mm block in a friend's driveway where the gates close.
The springs seemed to have settled a bit from new, so had the spring bases raised slightly. Is now 106 mm / 4" in the centre of the splitter.
Hopefully I will get to have a look at a lot of different TVRs at Chatsworth this year. I have only been to one local TVRCC meet since getting the car 14 months ago and there were no other T cars.
Sevenman said:
Tamora seemed plenty low to me...
When I first got the car, I scraped the centre of the front splitter on a 3" / 75mm block in a friend's driveway where the gates close.
The springs seemed to have settled a bit from new, so had the spring bases raised slightly. Is now 106 mm / 4" in the centre of the splitter.
Hopefully I will get to have a look at a lot of different TVRs at Chatsworth this year. I have only been to one local TVRCC meet since getting the car 14 months ago and there were no other T cars.
Be nice to meet up with you there. We'll either be in our Tamora or Sagaris (weather dependant...)When I first got the car, I scraped the centre of the front splitter on a 3" / 75mm block in a friend's driveway where the gates close.
The springs seemed to have settled a bit from new, so had the spring bases raised slightly. Is now 106 mm / 4" in the centre of the splitter.
Hopefully I will get to have a look at a lot of different TVRs at Chatsworth this year. I have only been to one local TVRCC meet since getting the car 14 months ago and there were no other T cars.
RedSpike66 said:
my T350 used to bottom out a hell of a lot even on the M40 through Oxfordshire, so perhaps they all have this generic design problem.
Mine wasn't as bad as this but my understanding is that they were all softer at the rear than the front. This accentuated the weight shift rearward when you accelerated; increasing grip and improving standing start acceleration. I've blanked on what this is called - it's not axle tramp but someone will know (?roll stiffness). My experience was that it was more likely to lose grip exiting a bend on a constant throttle, sliding as if it were on ice than if I gave it the beans. When fitting my nitrons, Topcats have dramatically stiffened the rear. I can't say I've noticed any reduction in straight line grip but my confidence in cornering has increased a thousand-fold now that the rear isn't rolling around.jrb43 said:
When fitting my nitrons, Topcats have dramatically stiffened the rear.
Do you know what spring rates they used to accompany your Nitron dampers?More generally, it would be useful to build up some knowledge of the range of spring rates used from factory standard to the different suspension kits.
Does anybody have any information? All I can share is that Gaz Gold Pros should come with 400/350 lb/in springs front/rear for the Tamora/T350.
Sevenman i posted last year regarding a similar issue with my newly fitted Protechs, I don't know if there is anything of use in this thread, but it might be worth a read.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Sevenman said:
jrb43 said:
When fitting my nitrons, Topcats have dramatically stiffened the rear.
Do you know what spring rates they used to accompany your Nitron dampers?More generally, it would be useful to build up some knowledge of the range of spring rates used from factory standard to the different suspension kits.
Does anybody have any information? All I can share is that Gaz Gold Pros should come with 400/350 lb/in springs front/rear for the Tamora/T350.
Well to be fair the rear aero is on, and the front isn't... 
Pursyluv said:
Sevenman i posted last year regarding a similar issue with my newly fitted Protechs, I don't know if there is anything of use in this thread, but it might be worth a read.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Do you know what spring rates your Protechs came with? Might need to go back to Protech to find out.http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Don1 said:
Watching this with interest, as two up and at speed on an A road, I got the tyres rubbing in the Tamora with Gaz Golds yesterday, a few times...
I think I have only had it rub when 2-up, but as the car is quite often like that, I would like to avoid it.Might be that the stiffer springs will do the trick. I still have some questions about the Gaz Gold damper length though and it would be interesting to know how much damper travel is left on T350s/Tamoras with different setups. A wander through a TVR Specialist with a number of cars up on ramps would be interesting for comparison.
Sevenman said:
Pursyluv said:
Sevenman i posted last year regarding a similar issue with my newly fitted Protechs, I don't know if there is anything of use in this thread, but it might be worth a read.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Do you know what spring rates your Protechs came with? Might need to go back to Protech to find out.http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Pursyluv said:
Fronts are 375 or 400 (he wasn't sure) and the rears are 325 - he said maybe i should have specified stiffer springs if i was going to drive the car fast
indeedFrom what I have found out so far, 325 is considered too soft for the rear (although may be used on the Chimaera).
Fast doesn't really come into it. Hitting some awkward road undulations at the speed limit is enough to cause wheel rubbing.
If it's just the tyre catching the inner arch cant you reprofile the inner arch? we do it on cerbs and chims a lot when they catch.
Other than that: the gaz has relatively low levels of low speed compression damping, so this isn't helping. The downside is that the damping ramps up aggressively at high speed piston movements, which means when you add extra spring rate the ride quality suffers.
Getting creative with a slightly stiffer spring and a proper length bump stop might cure it for you. I don't know why you think a shorter damper will help though, that would mean that for any given ride height the damper top would be further from the bump stop, so the extra effective spring stiffness that comes from the bump stop will be delayed in action, making your rubbing issue worse not better.
Choose a spring rate that gives you the handling and basic ride you need, then spec the bump stop to keep the car from bottoming out.
Other than that: the gaz has relatively low levels of low speed compression damping, so this isn't helping. The downside is that the damping ramps up aggressively at high speed piston movements, which means when you add extra spring rate the ride quality suffers.
Getting creative with a slightly stiffer spring and a proper length bump stop might cure it for you. I don't know why you think a shorter damper will help though, that would mean that for any given ride height the damper top would be further from the bump stop, so the extra effective spring stiffness that comes from the bump stop will be delayed in action, making your rubbing issue worse not better.
Choose a spring rate that gives you the handling and basic ride you need, then spec the bump stop to keep the car from bottoming out.
spitfire4v8 said:
If it's just the tyre catching the inner arch cant you reprofile the inner arch? we do it on cerbs and chims a lot when they catch.
What does that involve?spitfire4v8 said:
Getting creative with a slightly stiffer spring and a proper length bump stop might cure it for you.
Agreedspitfire4v8 said:
I don't know why you think a shorter damper will help though, that would mean that for any given ride height the damper top would be further from the bump stop, so the extra effective spring stiffness that comes from the bump stop will be delayed in action, making your rubbing issue worse not better.
It 'looks wrong' to have so little damper travel before it hits the bump stop. It and could mean that the damper is only operating at one extreme of its motion rather than normally being in the middle of the travel - but none of that might be a problem.What I think I want from the suspension is a linear spring rate through the range of motion of the wheel. This spring rate needs to be sufficiently stiff to avoid rubbing / hitting bump stops.
I want to use the extra effective spring rate from the bump stop only on very rare occasions.
Hitting a bump stop must be a bad thing for handling purposes. Rather than having a linear spring rate through the wheel travel it suddenly changes from linear to much stiffer with a possible loss of traction. When dealing with bumps round corners it may cause the wheel to skip rather than follow the road. Someone who knows much more about suspension than me might understand the implications.
The current setup makes it appear as if the car is using the bump stop for support in everyday driving, and sometimes quite a lot of bump stop when the wheel rubs. I would rather it only used the bump stop very rarely (as should be the case). This might be acheivable with a shorter bump stop and a stiffer spring rate so it is less likely to reach it.
If you're running std gaz springs then you already have a linear spring rate, it's the wheel rate you need to be concerned about, which isn't a linear rate.
The last thing you need is a bump stop that only comes into effect just before the tyre hits the inner arch, or just before the fibreglass undertray hits the tarmac .. that sudden increase in wheel rate will upset the car just when you're on the limit of suspension travel. What you really want is a bump stop that comes into action progressively so you tend to not feel its action so much, but the good thing about rubber/poly bump stops is that their action is rising rate and can be made massively more so by their shaping, so if you have a stiff bump stop the further you squish them the more effective wheel rate you get which offsets the natural falling rate of the inclined spring on the wheel rate.
On re-profiling the inner arch for more clearance just go to any of the bodyshops in your area who do fibreglass repairs and get them to chop out the inner arch fibreglass where the tyre is rubbing and reshape the fibreglass to allow more tyre clearance.
The last thing you need is a bump stop that only comes into effect just before the tyre hits the inner arch, or just before the fibreglass undertray hits the tarmac .. that sudden increase in wheel rate will upset the car just when you're on the limit of suspension travel. What you really want is a bump stop that comes into action progressively so you tend to not feel its action so much, but the good thing about rubber/poly bump stops is that their action is rising rate and can be made massively more so by their shaping, so if you have a stiff bump stop the further you squish them the more effective wheel rate you get which offsets the natural falling rate of the inclined spring on the wheel rate.
On re-profiling the inner arch for more clearance just go to any of the bodyshops in your area who do fibreglass repairs and get them to chop out the inner arch fibreglass where the tyre is rubbing and reshape the fibreglass to allow more tyre clearance.
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