GTR Chassis

[ouagadougou]

Hi all,

I havent had the chance to try a GTR yet personally however a friend of mine has tried a couple on the track and wasnt impressed by the chassis stiffness !!

Having checked in here I cant find any major comments about this and I was wondering if anyone had any words of wisdom ??

Cheers.

[Fast BMW 7]

If you want to get an opinion of the merits of the GTR chassis, see Jay's site on his GTR.
His opinion of the chassis was that it was a very flexible chassis that was very stiffly sprung to compensate and had questionable roll centers to boot.
See his website to see what he did to augment the chassis in order to control the torisional flex.
www.ultimav12.ca/
I think he is still playing about with the suspension to address the roll center issues!
Cheers. Harry.

[bluesatin]

Shame to see negative comments from two people who have never owned or driven an ultima!

[andygtt]

Does the chassis flex and does it handle? what are you comparing it with?

OK well having owned one.... the chasis doesn't appear to be the stiffest in the world, but it easily handles well over 500bhp and remains easy to drive on the road, so it's a package that works.


Does it handle? well it was better than my M3 and I wouldn't say it was worse than our Boxter just different. But these are very different cars and much heavier so not a real comparison.

However I had a VX220 straight after selling the Ultima (very similar concept but with no power) and I would say the VX was better at low speeds but the Ultima was better at high speeds as it actually has downforce aids unlike the VX.


What I'd say is go to the factory and get Ted to take you out in one... you won't come back with the same questions.

[ouagadougou]

My original question is not a criticism and is not meant to appear negative towards the GTR in any way. I quite fancy a GTR as a self build project but before departing down that road I would like to gather some more information and clarify a few things first. I prefer to be armed with a few facts and not speculative rumours before approaching the factory. Pistonheads seems a good place to get a better picture from real owners so thanks to those that have had real GTR experience for the responses.

[Fast BMW 7]

As an owner and builder of a unique GTR, I believe Jay is entitled to his own opinion, even if the rest of us choose to disagree on some level with him.
Lee was only requesting for some opinions and Jay certainally is not short of opinions.
Cheers! Harry.

[Stig]

It does make me chuckle when people come out with this. I assume that your friend must have a lot of race car experience (and be a pretty accomplished driver), as most mere mortals would struggle to identify chassis flex against incorrect tyre pressures, unsuitable damper settings, spring rates, not being strapped in to the seat properly etc.etc.etc.

Jay did a lot of work stiffening up the car, which is fine if you want to. However, he did most of the testing before panelling the chassis. This alone makes a massive difference to the torsional stiffness of the chassis, let alone fixing the body on afterwards which also helps.

Nothing wrong in making it as stiff as hell, but consider where you'll be spending most of your driving - on the road? Well, unless you want to lose all your fillings, a mega-stiff chassis may not be the panacea that you might think it is

Best advice is to try before you buy. I think you'll be satisfied that it's plenty good enough as it is

[bluesatin]

Further to stigs e-mail I think Jay modified the chassis to accomodate the engine then stiffened it!

[chuntington101]

how do the race teams get along with the chassis? do they do any work or race as stock? also what about the Stealth B6, i read that ran an GTR chassis but front the limited pics i have seen they dont use the two 2 saports coming from the roll cage to the rear suspension mounts.

thanks Chris.

[cymtriks]

Stig said:

It does make me chuckle when people come out with this. I assume that your friend must have a lot of race car experience (and be a pretty accomplished driver), as most mere mortals would struggle to identify chassis flex against incorrect tyre pressures, unsuitable damper settings, spring rates, not being strapped in to the seat properly etc.etc.etc. Jay did a lot of work stiffening up the car, which is fine if you want to. However, he did most of the testing before panelling the chassis. This alone makes a massive difference to the torsional stiffness of the chassis, let alone fixing the body on afterwards which also helps. Nothing wrong in making it as stiff as hell, but consider where you'll be spending most of your driving - on the road? Well, unless you want to lose all your fillings, a mega-stiff chassis may not be the panacea that you might think it is Best advice is to try before you buy. I think you'll be satisfied that it's plenty good enough as it is

If you make the chassis "as stiff as hell" then you have the option of lowering the spring rates to improve the ride. This in turn often improves the cornering and handling because the suspension works better if it is actually allowed to suspend the car as opposed to simply transfering loads through a relatively rigid set of links into a floppy chassis. Suspension always works best with a stiff chassis for both ride and handling.

The Ultima chassis is no more efficient in terms of stiffness for its weight than a simple X braced ladder frame.

It would be difficult to improve due to the need to route tubes around the engine. Jay gets round this by putting an X brace OVER the engine to the roll cage. Ok for a coupe but no solution if you are planning a spyder version. A ladder frame rear section would be a reasonable solution though and would free up enough width to permit bigger engines than the SBC or to allow a rethink of the exhaust which might gain a few bhp.

All that doesn't stop the current chassis working perfectly well though. As long as the factory and the customers are happy there's no need to change.

[andygtt]

bluesatin said:

Further to stigs e-mail I think Jay modified the chassis to accomodate the engine then stiffened it!

correct, but he measured the raw chassis stiffness before he modded it and after (ie before he cut anything)!

[chuntington101]

just thinking about this the other day. would it be possiable/fesable to "beefup" the standard chssis with ally honeycombe? you could mount a sheet (or several) of 1 inch think stuff on the bottom of the car (like TVR did with the Typoon) and then stick sections of honeycomb in between the lader arangements. anyone know if the later would work? also you could use it for the bulkhead and to beef up the front and rear suspension points.

dont think it would add TOO much wieght (say 50kg) and could make a real diffreance.

thanks Chris.

[adequatespeed]

There are some interesting modifications on Jay's site, which I would consider if i was building another Ultima. Every improvement is a valid one.

Most useful seem to be the cross brace near the steering coloum, the X brace between the roll bars (I dont this this is possible if using a chevy due to the distributor, carb and air filter), the plate in the roof and the brace near the gearbox. All of these are simple low cost modifications well within the realm of a home workship, given a welder and some steel tube.

It would be interesting to see how the Ultima compares to cars like TVR, Turner LMP and Westfields XTR2, which employ similar construction techniques.

What are they like in terms of tortional rigidy?

This is not a dig at any other car, but comparitive information is essential beore anyone can say either car is flexy

[gtr-gaz]

Surely, Maclaren would not have used it as a test bed for there F1 road car engine, if it was not up to the job?

Gary

[DHGTR]

i think we have to remember that this chassis is built to a certain specification and also a certain acceptable price. i am sure that the Factory would not disagree that the rigidity and strength of the frame could be improved but you must also bear in mind this is not a race car and Ultima do not pretend it is. It is one of the best performing 'road' cars on the market put together into a package that a capable diy'er can build for a fracton of the price that other 'supercars' demand. If you remember a couple of months ago Colin Blower was selling his racer and wanted £80k, this isnt all down to the race engine and i have heard the car actually cost around £1/4 million to get to race readiness. Some of you may feel that the the Ultima should be using the best of everything to assemble but i for one am glad it uses very good components and can be built for a relatively reasonable price.

wow this is getting to start sounding like a rant. i ought to unwind a bit after work before chipping in my twopennuth

[chuntington101]

i agree. i think we should all have at least 2 pints (or doubles) before we post!

be interesting to see what the race teams do though to make the chassis stronger! where are the main areas whhere flex happens?

thanks Chris

[cymtriks]

chuntington101 said:

i agree. i think we should all have at least 2 pints (or doubles) before we post! be interesting to see what the race teams do though to make the chassis stronger! where are the main areas whhere flex happens? thanks Chris

Since you asked-
The rear suspension region is not fully triangulated. This would be fairly simple to put right.

The engine bay top relies on the triangles at the back of the sills which could be made more effective or the entire engine bay region could be redesigned along ladder frame principles which would probably be no heavier but simpler and cheaper.

The front suspension region would benefit from more triangulation.

Jay Esters mods cover these regions.

The chassis could probably be made simpler, cheaper and stiffer but this would incurr the cost and complication of redesigning a lot of the car to do this.

I did some FE analysis on a ladder frame and spaceframe chassis for a mid engined car but had to shelve the idea due to the cost and complication of making the bodyshell.

The spaceframe weighed about 65lbs (30kg) less than the ladder frame and was a very similar stiffness. The ladder frame allowed easier entry, was simpler, cheaper and allowed more engine options.

For an Ultima sized car the spaceframe tubes would need to be bigger so the frame would probably be around the same weight as the ladder frame but about 50% stiffer. This assumes that the tubes would fit round the engine which might be impossible for a big V8.

[ultimichael]

For those who haven´t yet seen it, here´s an example of what racers do to the Ultima chassis.

www.qvickmotors.com -> Gallery -> Ultima Project.

Some mods are similar to Jay´s.
They reinforced most corners in the engine bay.

Michael

[shithotfast]

try two viagra in each petrol tank! should stiffen things up!

[chuntington101]

is there any way you could use the engine and box as stressed componets like they do in race cars? the block (SBC) should be able to take a bit of force andeould recuce the need for braces around the engine. as for the box i dont know. but if you could it may increase the regidity of the rear suspension.

thanks Chris.