Brakes

[p.mole1]

I have the standard Triumph calipers fitted to the front of my Caterham and the AP racing mastercylinder. The feel of the brakes and balance is superb however since the engine has been upgraded to just short of 200bhp they are lacking a little bit on track days. Do the higher performance Caterhams have vented front discs? I have 13 wheels so there is not a huge amount of room to fit a larger rotor. I am concerned that if I fit a 4 piston caliper I will ruin the brake balance. 

Ideally I would like to fit a larger rotor or a vented rotor with a 2 piston alloy caliper, I found a company that supplies all types of different alloy calipers with all sorts of piston combinations ( can't remember the name ) but I have not got a clue, there seems to be so many options.

[SM25T]

HiSpec in Dartford ? I fitted their 4 pot Ultralite calipers with solid 260mm front discs.

[p.mole1]

Thanks, that's the name I couldn't remember!, are you using 13 inch wheels?

[SM25T]

No, 15" ... but there is plenty of room around the caliper .... I measured it for someone that had 13" wheels.

[Guy Lowe]

The standard calipers will be fine for >200HP on track, upgrading is a total waste of money. Roger Ford put up a very helpful post a couple of years back (yes I have searched for it ) about how Caterham Graduates race cars with standard calipers and discs never have any problems with heat or fade and I'm sure they put greater demands on their brakes than the average track day warrior does, just put some Mintex 1144 pads in the fronts and run standard pads in the rears IMO.

[Geoff Brown]

BUT - ensure that the balance weights on a 13" wheel are strategically positioned or the corners will be knocked off the caliper. 

Trust me I know !

[p.mole1]

Thanks I'm running Mintex 1144 in the rear and Ferodo DS 2500 in the front, they seem to lack bite and require an extremely large amount of pedal pressure however the pedal travel is almost zero. Probably the result of the master cylinder.

My back brakes seem to run very hot the discs turn blue and also the pad wear is faster at the rear, but this is probably down to the compound. I have felt the brakes go off a bit at Croft but it has 2 long straights and this was with a standard screen, I was worried about using an areo screen due to the reduced drag. The brake balance seems fine with a slight bias to the rear  under maximum braking.

[7 wonders of the world]

I took the AP 4 pots / vented discs off and now run Hi Spec UL4 up front and SVA UL2 at the rear both on stock drilled 9" discs with the AP M/C, I found 1144's a little dead in feel, great from cold but lacked feel higher up he temperature range.

I now run DS3000 all round and have consistent feel and a great pedal with lots of feel and feedback.

Significant saving in rotational and unsprung weight too compared with stock AP front and sierra rears  

[Guy Lowe]

 

My back brakes seem to run very hot

That's quite normal and I get through about 3 sets of rear pads to one set of fronts, that's why I say standard front calipers are adequate for fast road/track driving.

Guy

p.s. I do about 800 miles per year, all track day mileage, I don't use my car on the road much  

 

[Guy Lowe]

DP

[rj]

The rear brakes work a lot harder on a Seven, than they do on a tin top.
The weight distribution is close to 50:50 and the COG is low, so the mass displacement will not be as significant as in the tin top.

Be very careful not to upset the balance if you change anything. It took me years to regain balance after having fitted uprated fronts - to save my knee, not becuase the brakes ran hot!

[aerobod - near CYYC]

I have found that I have better brake balance with the standard Caterham pads on the front AP 4-pot calipers and Ferodo DS2500 rear pads on the single-pot calipers, I was getting too little rear braking before front lock-up with the blue-dot rear pads with slicks on the track. Also the blue-dot pads were wearing at 5x the rate of the front pads.

One thing I caution those who are new to using the Caterham on the track is that you can lose a lot of torque on the rear wheel nuts due to the heat from the brakes. After swapping from road wheels to track wheels I will normally lose 25Nm (85Nm down to 60Nm) in the first 30 minute track session, then after re-torquing about 5Nm after the second 30 min session, after that the nuts will stay at 85Nm. This is actually less of a torque loss than I used to have before carefully scraping all the powder coat off the mounting face of the 13x8 rear wheels, as supplied by Caterham. I've never experienced more than a 10Nm torque loss on the front wheel nuts. I normally check the wheel nut torque before going out to the next session, to allow the hubs to cool as much as possible. Although there is some rational to not torquing to the standard spec unless the hubs have absolutely cooled down, I don't feel that less than 60Nm is a high enough torque when the hubs are hot and the Ford specs on 4x108 PCD hubs could be as high as 100lbft / 135Nm, so even if the cold torque could be 110Nm for a hot torque of 85Nm, it is still well within any reasonable safety factor.

[Wrightpayne]

James,

The heat torque loss in interesting. Do you have to back them off when you have finished your trackday so they dont end up over torqued as everything cools down?

Regards

Ian

[elie boone]

At Croix in France the limit for std brakes is 150bhp above that you need vented rotors. BTW Hi-Spes does a vented rotor for 13" wheels

[aerobod - near CYYC]

Hi Ian,

The cold torque is higher after hot torquing to the same 85Nm, but difficult to measure accurately as the break away torque when loosening is lower. I'm just a bit wary that the Caterham torque is quite low for the M12x1.5 studs and 4x108mm PCD used by other manufacturers, so the hot torque loss is a high proportion of the initial torque. I would say at least 75Nm hot would be a good minimum, as that is the old Caterham cold wheel torque spec before they changed it to 85Nm.

Usually the next day after a track day I swap the 13" track wheels with slicks back to the 15" road wheels with 'R' compound tyres and torque those wheels to 85Nm cold.

As I had a track day Sunday and haven't swapped the wheels back yet, I just went and measured the loosening break away torque on all the wheel nuts, it is currently 60Nm on the fronts and 75Nm on the rears after starting at 85Nm cold in the first session on Sun, then re-torquing as necessary before each subsequent session. I just also loosened each wheel nut are re-torqued to 85Nm and then measured the loosening break away torque as 65Nm on those freshly cold torqued nuts.

[Bricol]

I would guess Caterham's suggested lower tightening torques take into account aluminium front hubs, and thinner rear hubs than ones holding the wheels on a 2 tonne Ford with heavy 20" wheels - its the whole bolted joint loading being taken into account.

I would guess the joint loading loss after the first session is more to do with the wheel/hub/nut joint settling in - much as you are advised to check wheel nuts after a few miles following having tyres changes rather than temperature induced changes in stud length - tightening torque should take usual temperature changes into account, and without doing the maths on the Youngs Modulus change, I'd be a little careful

Your day old crack-off torque figures aren't following usual theory of increasing - might be worth checking both the torque wrench, and the stud threads against a good quality pitch gauge.

 

[aerobod - near CYYC]

To be clear, the "crack off" / "break away" torque is for loosening, it would increase for tightening due to the static torque value being higher than the dynamic torque when the torque wrench is tightening and initially clicks. The torque wrench has been checked for calibration and consistency last year and I've experienced the same effect in the same way on my R400 since 2013 when I first took it on the track.

Also, bearing in mind that the threads are kept very clean and smooth and the aluminium cone washer that Caterham provides helps reduce the cone seat friction quite a bit. With clean dry threads on any wheel bolt or nut I have never found the loosening torque to exceed the tightening torque unless the threads are corroded or dirty on any vehicle I have checked.

Wheel nut/bolt torque loss on wheels during track use is common on any vehicle. Last month we had a Mclaren 720S lose a wheel just coming into the pits due to torque loss on the bolts towards the end of the day. The owner had checked the bolt torque before taking the car on the track. A couple of years ago a Turbo Beetle was driving past us in the paddock when he braked to turn into his spot and the front left wheel just kept on going.

[p.mole1]

Thanks , something to think about. I have never driven any other Caterhams so I have nothing to compare it to. I have suffered some minor brake fade at Croft before at a non Caterham track day but I was leaving the braking to the last minute, not the best driving. In theory my front brakes should have more power as I have gone from a 185/60 14 to a 185/60 13 which is a smaller diameter. 

[elie boone]

On a Caterham the wheel is not supported by the hub, it's supported only by the bolts. That gives more strain on the bolts therefore i do them up at 100Nm, never lost a wheel or had to fasten a wheel nut during a track day. I do have to say that i only use wheel with steel inserts.