In the sixth part of our han­dling se­ries, Neil re­veals all you need to know about tie rods and how they can ef­fect your Mini.

In the sixth part of our han­dling se­ries, Neil talks about tie rods, and how they have a mas­sive im­pact on how a Mini han­dles…

Mini Magazine - - Contents -

Tie rods are of­ten re­placed on Mi­nis. One rea­son is that the orig­i­nal parts of­ten end up bent by peo­ple jack­ing the car up on them, but I sus­pect that a lot are up­rated sim­ply be­cause they don’t look very sturdy. Hap­pily, the stan­dard part is up to the job in nor­mal cir­cum­stances as most of the forces acted on it are pulling along the length of the shaft rather than try­ing to bend it. If you are us­ing the Mini in more ag­gres­sive sit­u­a­tions then you may find the need for stronger tie bars but you are also ad­ding more weight.

The tie rod does more than sup­ple­ment the bot­tom arm mount­ing, it also sets what is known as the cas­tor an­gle (or ‘caster’ for our Amer­i­can cousins). You will be fa­mil­iar with cas­tors on shop­ping trol­leys and how im­por­tant the mount­ing point is to where the wheel wants to go and how it “self cen­tres”.

The tie bar com­pletes a tri­an­gle formed with the bot­tom arm and

“If you are us­ing the Mini in more agres­sive sit­u­a­tions you may need stronger tie bars”

sub­frame, so chang­ing the length of the tie bar al­ters the an­gle be­tween the bot­tom arm and the sub­frame. Think­ing about this tri­an­gle, you can see that putting longer bot­tom arms on, for ex­am­ple, will need longer tie rods to keep the same an­gle be­tween the bot­tom arm and the sub­frame.

AD­JUSTABLE TIE BARS

It’s the self cen­tring ef­fect which we can change with ad­justable length tie bars and this ad­just­ment be­comes a must when you mod­ify other as­pects of the sus­pen­sion. The steer­ing self-cen­tring is gen­er­ally a good thing, but like ev­ery­thing else it can get to a point where it just causes prob­lems. If you moved the front wheels too far for­ward they would want to turn in every di­rec­tion apart from straight, where if you move them too far back, then they would re­sist your de­sire to go around any cor­ners.

A good start­ing point when you fit ad­justable tie bars is to match the stan­dard length items. That will give you a point to com­pare ad­just­ments to. Make sure that any mea­sure­ments are made from the mount­ing points of the

bars, not the over­all length as the re­place­ment tie bars may have dif­fer­ent length threads on them and there­fore dif­fer in length even if the sus­pen­sion ge­om­e­try is the same.

There are a cou­ple of dif­fer­ent ways of mount­ing tie bars on to the front of the front sub­frame. The fac­tory units use a threaded end with rub­ber ei­ther side. This al­lows a lit­tle move­ment at the sub­frame end which is needed as it also acts as a bear­ing for when the wheel moves up and down. There are al­ter­na­tives to rub­ber, in­clud­ing stiffer bushes. Th­ese stiffer bushes are okay, and may be a so­lu­tion if you find that the tie rod is mov­ing too much un­der brak­ing for ex­am­ple, how­ever th­ese firmer bushes can per­ma­nently de­form and I’ve seen them split and fall off en­tirely when used on the top of rear dampers. Al­though they are trapped bet­ter in the tie bar mount you re­ally don’t want that to hap­pen there. I would rec­om­mend that you check any bushes made of dif­fer­ent ma­te­ri­als on a reg­u­lar ba­sis to en­sure that all is well.

ROSE JOINTS

For cir­cuit work and tar­mac ral­ly­ing, rose-jointed tie bars are avail­able. Th­ese give free ver­ti­cal move­ment to the tie bars and zero play. This is great in the com­pe­ti­tion en­vi­ron­ments as you can main­tain your ge­om­e­try pre­cisely whilst mak­ing sud­den changes from hard ac­cel­er­a­tion to heavy brak­ing. As ever though, there is a trade off; mainly that any hits your wheels take will get trans­mit­ted straight through to the tie rod mount­ing points on the front sub­frame. It’s en­tirely pos­si­ble for th­ese to bend, al­ter­ing your ge­om­e­try quite dras­ti­cally or even for them to break. Com­pe­ti­tion cars which use th­ese re-en­force the tie bar mount­ing points, this is also worth­while on a rally car us­ing any type of mount, par­tic­u­larly if you are ven­tur­ing into the forests.

The forces trans­mit­ted into sub­frames and body shells by us­ing firmer and solid mounts is a fac­tor which is al­ways worth se­ri­ous con­sid­er­a­tion. Solid

mounts also make the ride less pleas­ant over any sur­face im­per­fec­tions, al­though I sus­pect that most Mini own­ers are more in­flu­enced by han­dling and steer­ing re­sponse.

Tie bar length can cause your car to pull in one di­rec­tion un­der ac­cel­er­a­tion and brak­ing. The first thing to do is check that the mount­ing points are okay. The most likely cause is the tie bars are un­equal in length for some rea­son. If one is bent, you would be bet­ter to re­place it as you don’t want one fail­ing, and if you don’t know why it’s bent then con­sider a stronger ver­sion. If the bushes have too much move­ment then you can ex­pe­ri­ence pulling and it’s al­ways pos­si­ble for a sub­frame to be twisted in some way. You can carry out a de­gree of ad­just­ment to counter is­sues, but if you find you have to make big dif­fer­ences from one side to the other, or you need to keep mak­ing ad­just­ments then fur­ther in­ves­ti­ga­tion would be quite ur­gently re­quired.

Words and Pho­tog­ra­phy Neil Burgess

Ad­justable tie rod.

Rose-jointed tie rod.

Stan­dard mount­ing for a tie rod with up­rated bushes.

Re-en­force­ment on sub­frame mount­ing.

Tie rod ge­om­e­try.

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