this might be a dumb question but...
Discussion
at the risk of a public mocking for my complete lack of mechanical knowledge......
When autocar etc go on about " it has a great chassis " or the elise has a better chassis than a bmw what do they mean??? Obviously I know what a chassis is but how do they know when driving a car what is a good chassis? I've had a few sports cars and I know which which is quickest and which handles better but which one has the best chassis??
feel free to take the piss now...
When autocar etc go on about " it has a great chassis " or the elise has a better chassis than a bmw what do they mean??? Obviously I know what a chassis is but how do they know when driving a car what is a good chassis? I've had a few sports cars and I know which which is quickest and which handles better but which one has the best chassis??
feel free to take the piss now...
Basically they are talking about the combination of body shell and suspension components, which gives the car good handling, which is NOT the same as roadholding. Handling is how the car feels - is it composed under braking, cornering, acceleration, is the "feedback" you get from steering and seat good, that sort of thing, does it inspire confidence?
Road holding on the other hand is purely down to the tyres you use... a crap handling car can hold the road well if you put F1 slicks on it...., but that doesn't make it a good chassis.
Road holding on the other hand is purely down to the tyres you use... a crap handling car can hold the road well if you put F1 slicks on it...., but that doesn't make it a good chassis.
Not very helpful, but the 'feel' of a chassis is something that comes with driving a few cars, ie experience
In effect, you have to dial out suspension effects and behaviour to arrive at what the chassis is up to in terms of torsional stiffness etc, but basically some cars feel nailed to the road whereas others feel like they are floating on top of it.
For example, I drove an E38 M5 in the wet like a hooligan, then got into my 944S2 cabrio. The M5 was quite stiffly sprung, and the S2 quite softly sprung, but the M5 felt hugely distant and didn't feel like it was transmitting 'road information' despite the harder suspension. It felt like a wayward iron bed compared to the wonderfully communicative 944.
Outside of the seat of the pants driving feel, you can often test chassis rigidity by parking a solitary rear wheel on a kerb, then see how the doors shut! My Lotus Carlton had enough flex to cause the rear door to rub. Crrrap! Remember that the suspension is bolted to the chassis, so the geometry goes to pot if it flexes.
In effect, you have to dial out suspension effects and behaviour to arrive at what the chassis is up to in terms of torsional stiffness etc, but basically some cars feel nailed to the road whereas others feel like they are floating on top of it.
For example, I drove an E38 M5 in the wet like a hooligan, then got into my 944S2 cabrio. The M5 was quite stiffly sprung, and the S2 quite softly sprung, but the M5 felt hugely distant and didn't feel like it was transmitting 'road information' despite the harder suspension. It felt like a wayward iron bed compared to the wonderfully communicative 944.
Outside of the seat of the pants driving feel, you can often test chassis rigidity by parking a solitary rear wheel on a kerb, then see how the doors shut! My Lotus Carlton had enough flex to cause the rear door to rub. Crrrap! Remember that the suspension is bolted to the chassis, so the geometry goes to pot if it flexes.
There was some discussion of the torsional stiffness of the Elise in comparison to others here: www.pistonheads.com/gassing/topic.asp?t=3002&f=19&h=0&hw=torsional+stiffness 
"Handling is how the car feels"
IIRC
My definition of handling is the ability of the vehicle to react to changes in direction.
Roadholding is the ability of the vehicle to corner in any given direction, but not change in direction.
A chassis is a construction where all running components can be connected, the body is usually serparate.
Where the body is part of the floorpan, no chassis exists, this is known as monocoque construction
Regards
Big Rumbly
IIRC
My definition of handling is the ability of the vehicle to react to changes in direction.
Roadholding is the ability of the vehicle to corner in any given direction, but not change in direction.
A chassis is a construction where all running components can be connected, the body is usually serparate.
Where the body is part of the floorpan, no chassis exists, this is known as monocoque construction
Regards
Big Rumbly
quote:
Road holding on the other hand is purely down to the tyres you use
Somehow I think very few chassis designers would agree. Spring rates, damping, geometry, roll stiffnes, weight distribution and many other factors are at least as important as the rubber. A tyre that is not in contact with the road can have no influence upon roadholding.
As a practical experiment disconect a front and a rear shock absorber or tightly wedge a tree trunk between a suspension arm and the car body. Go for a drive and if you still think roadholding is purely a function of rubber I'll shave my beard off and post it to you.
if only it was just tyres!
quote:
quote:
Road holding on the other hand is purely down to the tyres you use
Somehow I think very few chassis designers would agree. Spring rates, damping, geometry, roll stiffnes, weight distribution and many other factors are at least as important as the rubber. A tyre that is not in contact with the road can have no influence upon roadholding.
As a practical experiment disconect a front and a rear shock absorber or tightly wedge a tree trunk between a suspension arm and the car body. Go for a drive and if you still think roadholding is purely a function of rubber I'll shave my beard off and post it to you.
- one beard to be posted then please.... They all affect the handling/feel/call it what you will.... and allow the TYRE to do what it does best . which is HOLD THE ROAD! Thats the common misconception, handling and roadholding are NOT the same thing.
If you keep the tyres the same but adjust other suspension components/make the body stiffer then the handling will be improved (or otherwise) which will have an effect on roadholding, because the forces on the tyre will be modified, allowing it to work properly. The reverse is also true. It is to a certain extent cause and effect, but I stand by my original statement NERH!
The beard is only on offer if you try my practical experiment and then still think its only tyres. Yes I have done the tree trunk trick as a get you home when a rear spring broke, we were in danger of blowing up the engine as the wheel spent so much time off the road allowing revs to soar.
Take the example of a Triumph Spitfire and an Elan Sprint. Same tyres and tyre size yes, same roadholding of course not, the Spitfire, in extremis tucks its rear suspension under and tries to corner on the sidewall, there is very little roadholding whereas the the Elan, nearly 40 years on is still a paradigm of chassis excellence.
Do you remember the beach buggy craze. We used to buy used F1 tyres from John Pearce and put them on the back wheels, lots of adhesion whilst the suspension remained around the static position, just as soon as there was any deflection the swing axle tipped the tyre onto one edge and hedgerow here we come.
Yes without tyres there is no roadholding but to use decent rubber you need to keep it in full contact with the road across its width, return it quickly to the road after a bump and, as far as possible keep it pointing in the direction of travel all functions of chassis design and fine tuning.
I can't see any posting that confuses roadholding and handling so it doesn't seem to be a PH misconception.
I'm hanging on to the beard for now!
>> Edited by gnomesmith on Saturday 3rd August 16:47
Take the example of a Triumph Spitfire and an Elan Sprint. Same tyres and tyre size yes, same roadholding of course not, the Spitfire, in extremis tucks its rear suspension under and tries to corner on the sidewall, there is very little roadholding whereas the the Elan, nearly 40 years on is still a paradigm of chassis excellence.
Do you remember the beach buggy craze. We used to buy used F1 tyres from John Pearce and put them on the back wheels, lots of adhesion whilst the suspension remained around the static position, just as soon as there was any deflection the swing axle tipped the tyre onto one edge and hedgerow here we come.
Yes without tyres there is no roadholding but to use decent rubber you need to keep it in full contact with the road across its width, return it quickly to the road after a bump and, as far as possible keep it pointing in the direction of travel all functions of chassis design and fine tuning.
I can't see any posting that confuses roadholding and handling so it doesn't seem to be a PH misconception.
I'm hanging on to the beard for now!
>> Edited by gnomesmith on Saturday 3rd August 16:47
I think we're generally talking about the same thing, just different terminology (trying desperately not to make this sound as though I'm giving in to superior knowledge! lol). Using one of your examples, the Elise (never driven one meself, but.......) reknowned to be a great handling car. If you then change ALL of tyres for an inferior type (whilst maintaining any size differentials front to rear) without changing the "chassis", then which will be affected - roadholding (grip) or handling.....
The general handling characteristics will remain the same (balance under braking, understeer, oversteer, whatever) albeit it at different speeds, but the roadholding will be impacted, because of the TYRE. Thats the point I was trying to make - yes I know that you can change a cars characteristics by adjusting bosy stiffness, camber, caster, toe-in/out, spring rates, bump/rebound rates, pick-up points, roll-centres, rollbar rates, C of G and these can improve the roadholding by allowing the tyre to do its job properly. Additionally, if you change the tyre balance front to rear (or side to side) then you will adjust the handling as well. Oh bugger it, its a complex subject, its Saturday and I need a beer!
quote:
If you then change ALL of tyres for an inferior type (whilst maintaining any size differentials front to rear) without changing the "chassis", then which will be affected - roadholding (grip) or handling.....
Okay we're both singing from the same song sheet and we'd agree on the answer to your question above, but Colin Chapman always considered the damper/spring combination to be the crux and to prove it he raced his early cars on some really naff rubber. If you really screwed up the damper/spring balance your grip would similarly go out of the window.
I'm about the join you with the beer so cheers!
PS. if you ever get the chance to drive an Elise and an Elan you'll find the Elise is more grippy but the Elan handles better and is, in my opinion, much more fun. The prospect of a 'new' Spydersport Elan with a Zetec is tempting me to cash in my Elite Climax fund.
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