HOW TO

Can re­ally build a race Mini for the road? We ex­am­ine bodyshell prep and sus­pen­sion com­po­nents in a bid to find the an­swer.

Mini Magazine - - Contents -

Back in the April 2018 is­sue we pub­lished a be­gin­ner’s guide to clas­sic Mini mo­tor­sport, look­ing at costs and how to get in­volved. We touched upon the con­trasts be­tween a race Mini to a road-le­gal Mini, sug­gest­ing that they’re out­wardly sim­i­lar yet me­chan­i­cally quite dif­fer­ent. So how dif­fer­ent re­ally is a road car to a cir­cuit racer and what’s to stop you from us­ing race-spec parts on the road, and vice versa? There’s much to cover, so let’s start with the big­gest com­po­nent – the bodyshell…

BODYSHELL

Aside from the fancy graph­ics and paint, there’s very lit­tle to dis­tin­guish most cir­cuit racing Mini bodyshells from their orig­i­nal road-go­ing state, at least upon first in­spec­tion. And re­al­is­ti­cally you could fully pre­pare a race Mini bodyshell, then use it on the road, but as will be a re­oc­cur­ring theme, that could be an ex­pen­sive route for not much gain.

In­te­ri­ors are fully stripped of all nonessen­tials and flammable fab­rics, the fac­tory bi­tu­men sound-proof­ing painstak­ingly re­moved from the floors, rear wings and roof. All the parts that make a Mini a tad more com­fort­able and civilised – squishy seats, the ra­dio, heater, sound-dead­en­ing pads and car­pet – they’re off the menu. The rear seats will no longer be of use, so th­ese are trimmed back mid­way and the rear com­pan­ion bins usu­ally re­moved for roll-cage ac­cess.

Where welded-in roll-cages are com­mon­place, the lat­est de­signs form the skele­ton of the car and are in­te­gral to safety. For a road car, if you fancy a rollcage it’s more prac­ti­cal to opt for a bolt-in de­sign, as it’s eas­ier to re­move for fu­ture rust re­pairs. But how safe is any type of roll-cage in road car? On one hand it will con­sid­er­ably strengthen the shell, on the other, it in­tro­duces lengths of hard steel tub­ing all around your head. So har­nesses and racing seats come highly rec­om­mended along­side a ’cage, mak­ing a quick visit to the shop that lit­tle bit more awk­ward. You’ll also need to con­sider switches and con­trols, and if you can still reach ev­ery­thing while strapped in.

Light­weight com­pos­ite pan­els can cer­tainly be used on both road and race Mi­nis to good ef­fect, al­though panel fit and vi­bra­tions can leave some­thing to be de­sired. On a racer, it’s ben­e­fi­cial to leave a

large gap around a com­pos­ite front end to the scut­tle panel, for ex­am­ple, as it saves wear­ing out the paint when it rubs. That’s go­ing to look quite agri­cul­tural on the road, plus you have all the road grime to flick up and out. Stan­dard steel front ends are ar­guably much bet­ter suited to a road car – bet­ter panel gaps, less vi­bra­tion, and stronger. Re­mem­ber that race Mi­nis rely on the roll-cage for strength, not the front end. An­other com­mon fit­ment to race Mi­nis are poly­car­bon­ate side and rear win­dows. Light­weight and shat­ter-re­sis­tant, they’re ideal for com­pe­ti­tion, but for reg­u­lar road use, even the fancy coated ver­sions will be­come scratched in time. Se­cu­rity is also ques­tion­able if you go for the slid­ing hatch front door win­dows.

Tubbed rear arches are com­mon­place across all low­ered Mi­nis, and done prop­erly make a sensible long-last­ing mod­i­fi­ca­tion, if that’s your thing. Mod­i­fy­ing the bulk­head for a large air­box, how­ever, is in­creas­ingly be­com­ing a prob­lem at MoT time, so that’s one mod best left to the race cir­cuit, in the UK at least. Rear valance re­moval, well, that’s only ad­van­ta­geous on the road if you’ve mod­i­fied the rear cones to ac­cept a hex bar ad­juster in­side the Hi-Lo sus­pen­sion plat­forms. That leads us to…

SUS­PEN­SION

To ad­just the rear right height eas­ily, with­out jack­ing the car in the air, the rub­ber cones have their cen­tres drilled out, through the threads that usu­ally grip into the cone

com­pres­sion tool up front. The pur­pose is to be able to more pre­cisely set up cor­ner weights to per­fect the car’s bal­ance. On a road car that’s usu­ally in vain as there are so many vari­ables, from pas­sen­gers to lug­gage, and to re­ally no­tice the dif­fer­ence you need to be on the limit of ad­he­sion.

Sure, ad­just cor­ner weights on a racein­spired road car if you like, but you needn’t worry too much about ad­just­ing the ride heights in situ, as a ball­park setup will do the trick. In­stead, save some work of drilling cones and the front tower bolts by tweak­ing ride height on the ex­ter­nal Hi-Lo ad­justers in­stead. Also con­sider what’s prac­ti­cal in terms of ride height for the road, where speed bumps and pot holes can give a bru­tal re­minder of low ground clear­ance on a reg­u­lar ba­sis. Rub­ber cones can also sag con­sid­er­ably over time.

Dis­count­ing coilover con­ver­sions for the road due to their in­her­ent short-spring harsh­ness, you’ll re­quire more sup­ple sus­pen­sion of­fered by stan­dard-spec rub­ber cones. Rac­ers tend to use yel­low (full com­pe­ti­tion) or red spot (race/rally) cones; red can be okay on a fast road car but yel­low will likely be far too harsh.

This harsh­ness is also largely de­pen­dant on the dampers. Start at the half­way point on ad­justable dampers, then work from there to find the right bal­ance. Race dampers tend to fea­ture shorter fully open lengths to re­duce sus­pen­sion droop. They can also cost a small for­tune, with bil­let al­loy bod­ies and any­where up to four-way ad­justa­bil­ity to

con­trol bump and re­bound. On both counts, this can be overkill on the road, es­pe­cially when there are so many af­ford­able sin­gle ad­justable road damper units to choose from.

Anti-roll­bars are cer­tainly wor­thy of both road and com­pe­ti­tion Mi­nis, but the level of stiff­ness re­quired on a heav­ily sprung ag­gres­sive racer is far greater than on coun­try lane week­end toy. It’s a com­mon mis­con­cep­tion that race Mi­nis all run both front and rear anti-roll­bars – it’s usu­ally one stiff rear bar only, the ef­fect be­ing to re­duce un­der­steer by im­prov­ing front end grip. It pro­motes lift-off un­der­steer so the car can be bal­anced on the throt­tle through each cor­ner, cock­ing an in­side rear wheel in the process. You don’t re­ally want to be ex­pe­ri­enc­ing that on the daily com­mute, so a good tip for the road would be to run the sus­pen­sion and soft as pos­si­ble, then in­vest in small di­am­e­ter front and rear bars to re­duce body­roll. We’ve tried this setup in the past with Smootha Ride cones and a pair of ARBs and were suit­ably im­pressed.

Rose-jointed (rod end) sus­pen­sion com­po­nents are an ab­so­lute must on any race car to make the most of the avail­able grip, but on the road you’ll need to bal­ance up how harsh is too harsh. Re­mov­ing the rub­ber bushes gives a more pre­cise feel but less give in the sus­pen­sion. That said, we’ve driven many road Mi­nis with solid-mounted front sub­frames and Rose-jointed bot­tom arms and tie-rods, and it’s not any­where near as hard work as you’d ex­pect. Typ­i­cally, the harsh­ness comes from overly-stiff

dampers, run­ning the sus­pen­sion too low or with com­pletely knack­ered old rub­ber cones. If you do choose rod-end sus­pen­sion com­po­nents, as op­posed to those with rub­ber or polyurethane bushes, keep the joints clean and check reg­u­larly for wear. A race car is span­ner-checked af­ter ev­ery track out­ing, and there’s usu­ally some­thing worked loose! It’s also worth in­vest­ing in high qual­ity rod ends from known-good brands, as they’re stronger and more durable than bud­get-grade items.

WHEELS AND TYRES

The aim of per­fect­ing the sus­pen­sion setup is to max­imise tyre grip, so clearly tyres are a ma­jor con­sid­er­a­tion to the sur­round­ing com­po­nents and ge­om­e­try. Setup for a Mini Miglia on slicks varies wildly to a MkI on treaded his­toric tyres. One thing you’re un­likely to be able to trans­fer from race to road are the tyres them­selves, un­less of course it’s a race se­ries that stip­u­lates roadle­gal tyres only.

Ra­dial road-go­ing tyres are de­signed to last for many thou­sands of miles, and as such tend to be con­structed from harder rub­ber com­pounds than their racing coun­ter­parts. They’ll re­spond dif­fer­ently to changes in cam­ber, toe and caster, and setup can be al­tered ac­cord­ingly. They’re also not avail­able in the same widths, in 10- and 12-inch di­am­e­ters, see­ing as the Mini was orig­i­nally de­signed to run on 10x3.5-inch wheels. As a re­sult, if your dream is to run with 10x7-inch Mini Miglia split-rims on the road, the widest 165-sec­tion tyres avail­able can be­come in­cred­i­bly stretched. That’s not ideal as most tyre mak­ers stip­u­late max­i­mum wheel widths, so you could be in hot wa­ter, in­sur­ance wise, if you had an ac­ci­dent. It also doesn’t do the han­dling any favours to have a tyre hang­ing half off the rim!

Run­ning with race-width wheels on the road also has a ten­dency to in­duce tram­lin­ing, where the front tyres fol­low all the grooves in the tar­mac. To al­low fit­ment of seven-inch wide wheels, much neg­a­tive off­set – or ‘poke’ if you’re down with the kids – is re­quired. Mini Miglias get around the physics by some in­cred­i­bly in­volved

setup pro­cesses up front, the knowl­edge handed down over many gen­er­a­tions, but mainly a lot of time and ef­fort with string, pro­trac­tors and head scratch­ing.

The other two con­sid­er­a­tions with re­gards to us­ing race wheels on the road are main­te­nance and wheel arch ex­ten­sions. Many split-rim wheels use pol­ished bare alu­minium out­ers, and that takes some se­ri­ous ded­i­ca­tion and buff­ing to keep things look­ing pris­tine out on the road. Most will also re­quire wide arches and much trim­ming of the front wings for clear­ance on any de­gree of steer­ing lock.

With­out go­ing into a full sus­pen­sion ge­om­e­try setup fea­ture here, if you fit the same level of ad­justable com­po­nents to a road car, the pro­ce­dure is go­ing to be the same re­gard­less of the ap­pli­ca­tion. Ex­cept of course that ev­ery­thing needs to be more pre­cise on a race Mini, and that takes a lot of

time as you can chase your tail, es­pe­cially when cor­ner-weight­ing. A full pro­fes­sional sus­pen­sion setup by a Mini race spe­cial­ist can take an en­tire day, for ex­am­ple. There’s noth­ing stop­ping you from per­fect­ing road Mini sus­pen­sion ge­om­e­try in the same minute de­tail, but by the time you top up the fuel tank and bump up a kerb or two, ev­ery­thing changes.

So there’s a ba­sic out­line of the dif­fer­ences be­tween road and race, and the com­pro­mises re­quired. It’s not re­ally fea­si­ble to build a com­pet­i­tive race Mini for the road, and nor can you ex­pect a road Mini to per­form fault­lessly on track, but there’s cer­tainly much cross over be­tween the two. Next we’ll look at your op­tions when it comes to en­gine, trans­mis­sion and driv­e­train com­po­nents, and we should prob­a­bly look at brakes and an­cil­lar­ies too.

Road and race are two very sep­a­rate dis­ci­plines, so choose wisely when build­ing a fast road Mini – some up­grades are more use­ful than oth­ers.

2 Push­ing to the ab­so­lute limit on track re­quires pre­cise sus­pen­sion setup to per­fect the han­dling.

1 Cut­ting-edge Mini Miglia build in progress, where the welded-in roll-cage forms the struc­tural in­tegrity of the car.

All crea­ture com­forts are re­moved for safety, weight loss and a pro­fes­sional fin­ish. 4

3 Tubbed rear arches can be use­ful on all low­ered Mi­nis, to avoid tyre scrub­bing.

6 Light­weight doors and ex­te­rior pan­els can work equally well on road cars, but weight re­duc­tion is less no­tice­able stuck in traf­fic.

5 Al­though recog­nis­able as a Mini, the bodyshells are highly mod­i­fied for strength, han­dling and ease of re­pairs/main­te­nance.

7 Re­moved rear valance for easy ride height ad­just­ment.

8 Softer sus­pen­sion and spring re­place­ments are the way for­ward for road cars, at the ex­pense of body roll.

10 Th­ese rod-end-equipped lower arms from MED are aimed at mo­tor­sport use, but can po­ten­tially still be used on the road.

9 Fully-ad­justable length lower arms and tie-rods are used to per­fect the sus­pen­sion ge­om­e­try up front.

13 No room for your shop­ping in here! A flat car­bon fi­bre boot floor with reg­u­la­tion foam-filled fuel cell and in­te­gral anti-roll­bar.

Racing dampers like th­ese from Quan­tum are light­weight, highly con­fig­urable and re­build­able – beau­ti­ful but ex­pen­sive for a stan­dard road Mini. 11

Many parts on a race Mini are stan­dard by de­fault, or by reg­u­la­tions, whereas oth­ers are more ex­otic, like the split-rims and large rear anti-roll­bar. 12

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